The invention relates to a device for changing the operational state of an apparatus, in particular from a stand-by or power down mode into an active state.
Electronic devices are consuming electric power even when they are turned into stand-by or power down modes and thus energy is unnecessary wasted. For example, electronic devices with a man-machine interface, such as mechanic buttons or sensitive touch interfaces, need electric power to enable the wake-up to bring the device out of the stand-by mode into an active state. For capacitive touch screens for instance, a polling of the capacitance value can sense a touch on the surface leading to a signal for the wake-up of the system. Such a mechanism needs electronic components, such as dedicated microcontrollers. Even if these components are in power down mode, they are still power consuming when waiting for any input on the corresponding man-machine interface. Also other sensitive touch surface device technologies, such as resistive, surface acoustics waves or infrared, have wake-up capabilities that consume electric power when they are in stand-by mode.
One of the reasons why electric power is necessary is that the wake-up modules of these devices comprise sophisticated signal processing to be able to take the decision to wake-up a system following an analysis of the sensed input signals. To do this analysis, electric power is consumed which comes from the power supply. For remotely controlled electronic devices, it has been proposed to use the energy of the electro-magnetic waves received from the corresponding remote control unit, but for devices without a remote control, this solution does not make sense. In addition, to provide the electro-magnetic waves, the remote control unit itself consumes power.
Other remote controlled devices use the energy provided in air-borne sound to wake-up low power consuming elements. For electronic devices with a man-machine interface, this kind of wake-up is also not suitable as, in a noisy environment, the devices would be turned into an active state without a user having the intention to do so. Furthermore the generated energy level is typically too low for most of the applications.